1. Field of the Invention
The present invention relates to a display device including a thin film transistor at least in a pixel portion.
2. Description of the Related Art
In recent years, technology that is used to form a thin film transistor using a semiconductor thin film (with a thickness of from several nanometers to several hundreds of nanometers, approximately) formed over a substrate that has an insulating surface has been attracting attention. Thin film transistors are applied to a wide range of electronic devices like ICs and electro-optical devices, and prompt development of thin film transistors that are to be used as switching elements in image display devices, in particular, is being pushed.
A thin film transistor using an amorphous semiconductor film, a thin film transistor using a polycrystalline semiconductor film, or the like is used as switching elements in image display devices.
In addition, as switching elements in image display devices, a thin film transistor using a microcrystalline semiconductor film is used (Reference 1: Japanese Published Patent Application No. H4-242724 and Reference 2: Japanese Published Patent Application No. 2005-49832).